Method and apparatus to double LAN service unit bandwidth

ABSTRACT

A LAN Service Unit (LANSU) backplane extender provides an inexpensive way to increase LANSU backplane bandwidth so that the performance degradation that may otherwise result can be avoided. A system having increased LANSU bandwidth comprises a backplane including a plurality of data traffic communications connections operable to communicate data traffic, a Line Unit including a WAN interface and a data traffic communications interface to the data traffic communications connections, a LANSU including a LAN interface, a data traffic communications interface to a Bandwidth Extender, and a data traffic communications interface to the data traffic communications connections, and the Bandwidth Extender including a data traffic communications interface to the LANSU and a data traffic communications interface to the data traffic communications connections, the Bandwidth Extender operable to communicate data traffic between the data traffic communications interface to the LANSU and the data traffic communications interface to the data traffic communications connections.

FIELD OF THE INVENTION

The present invention relates to a bandwidth extender for a LAN ServiceUnit that increases LAN Service Unit backplane bandwidth.

BACKGROUND OF THE INVENTION

Synchronous optical network (SONET) is a standard for opticaltelecommunications that provides the transport infrastructure forworldwide telecommunications. SONET offers cost-effective transport bothin the access area and core of the network. For instance, telephone ordata switches rely on SONET transport for interconnection.

In a typical application, a local area network (LAN), such as Ethernet,is connected to a wide area network (WAN), such as that provided bySONET. The LAN and WAN may be interfaced by a device known as a LANService Unit (LANSU), which has ports for connecting the LAN and portsfor connecting the WAN. In many applications, the LAN input bandwidth tothe LANSU may be greater than the LANSU backplane bandwidth or the WANbandwidth that the system has to offer. If the traffic on the LANrequires greater bandwidth than the LANSU backplane or WAN can provide,traffic may be lost and serious degradation of performance may result.Proliferation of ever faster LAN technologies makes this situation evenmore likely. A need arises for a technique by which LANSU backplanebandwidth can be increased to handle increased LAN traffic bandwidththat is inexpensive and that avoids the performance degradation that mayotherwise result.

SUMMARY OF THE INVENTION

The present invention is a LANSU backplane extender card that providesan inexpensive way to increase LANSU backplane bandwidth so that theperformance degradation that may otherwise result can be avoided.

The invention involves a system having multiple cards which communicateacross a backplane using BW limited point to point links (communicationschannels). In the case where two cards A and B have more traffic thancan be carried from A to B over the existing communications channel anda communications channel exists from A to C and from C to B, C can beused as a Bandwidth extender by allowing its bandwidth to be used inparallel with A's bandwidth to create a wider communication channel toB.

In one instance the invention is implemented in a system having a dualstar architecture. The system has a LANSU communicating to both aworking and protect LU. The system has a communication channel from theLANSU to the adjacent slot.

A bandwidth extender is installed in the adjacent slot which enables anadditional communications channel from the LANSU to both the working andprotect LU.

In one embodiment of the present invention, a system having increasedLAN Service Unit bandwidth comprises a backplane including a pluralityof data traffic communications connections operable to communicate datatraffic, a Line Unit including a WAN interface and a data trafficcommunications interface to the data traffic communications connections,the Line Unit operable to communicate data traffic between the WANinterface and the data traffic communications interface, a LAN ServiceUnit including a LAN interface, a data traffic communications interfaceto a Bandwidth Extender, and a data traffic communications interface tothe data traffic communications connections, the LAN Service Unitoperable to communicate data between the LAN interface and the datatraffic communications interface to the Bandwidth Extender and tocommunicate data between the LAN interface and the data trafficcommunications interface to the data traffic communications connectionsand the Bandwidth Extender including a data traffic communicationsinterface to the LAN Service Unit and a data traffic communicationsinterface to the data traffic communications connections, the BandwidthExtender operable to communicate data traffic between the data trafficcommunications interface to the LAN Service Unit and the data trafficcommunications interface to the data traffic communications connections.

In one aspect of the present invention, the LAN Service Unit is furtheroperable to receive data on the LAN interface, split the received datainto two data streams, and transmit the data over the data trafficcommunications interface to the Bandwidth Extender and the data trafficcommunications interface to the data traffic communications connections.The LAN Service Unit may be further operable to receive data in two datastreams, one data stream received over the data traffic communicationsinterface to the Bandwidth Extender and one data stream received overthe data traffic communications interface to the data trafficcommunications connections, to reassemble the two received data streamsinto traffic data, and to transmit the reassembled traffic data over theLAN interface. The LAN Service Unit may be further operable to split thedata received over the LAN interface into a plurality of data streamsusing Virtual Concatenation, and wherein the LAN Service Unit isoperable to reassemble the plurality of virtually concatenated datastreams received over the data traffic communications interface to theBandwidth Extender and over the data traffic communications interface tothe data traffic communications connections.+

The LAN Service Unit may be further operable to split the data receivedover the LAN interface into a plurality of data streams using LinkAggregation techniques, wherein LAN data is separated based onindividual conversations defined by some or all of MAC SA, MAC DA, IPSA, IP DA and other higher OSI layer identifiers. The LAN Service Unitis further operable to reassemble the plurality of Link Aggregation datastreams received over the data traffic communications interface to theBandwidth Extender and over the data traffic communications interface tothe data traffic communications connections.+

In one aspect of the present invention, the LAN interface supportsEthernet and the WAN interface supports Synchronous Optical Network orSynchronous Digital Hierarchy.

In one embodiment of the present invention, apparatus for increasing LANService Unit bandwidth comprises a Bandwidth Extender including a datatraffic communications interface to a LAN Service Unit and a datatraffic communications interface to backplane data trafficcommunications connections, the Bandwidth Extender operable tocommunicate data traffic between the data traffic communicationsinterface to the LAN Service Unit and the data traffic communicationsinterface to the data traffic communications connections.

In one aspect of the present invention, the data traffic communicationsinterface to a LAN Service Unit is operable to communicate data with theLAN Service Unit. The data traffic communications interface to thebackplane data traffic communications connections may be operable tocommunicate data with a Line Unit having a WAN interface. Data trafficreceived from the LAN Service Unit may comprise one of a plurality ofdata streams formed by the LAN Service Unit by splitting data receivedover a LAN interface into two data streams. Data traffic transmitted tothe LAN Service Unit may comprise one of a plurality of data streamsthat are reassembled at the LAN Service Unit to form traffic data andtransmitted over the LAN interface. The data traffic received from theLAN Service Unit may be split using Virtual Concatenation or LinkAggregation, and wherein data traffic transmitted to the LAN ServiceUnit is reassembled using Virtual Concatenation or Link Aggregation.

In one aspect of the present invention, the LAN interface of the LANService Unit supports Ethernet and the WAN interface of the Line Unitsupports Synchronous Optical Network or Synchronous Digital Hierarchy.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of the present invention, both as to its structure andoperation, can best be understood by referring to the accompanyingdrawings, in which like reference numbers and designations refer to likeelements.

FIG. 1 is an exemplary block diagram of a system in which the presentinvention may be implemented.

FIG. 2 is an exemplary block diagram of an optical LAN/WAN interfaceservice unit included in the system shown in FIG. 1

FIG. 3 is an exemplary block diagram of a system in which the bandwidthextender of the present invention may be implemented.

DETAILED DESCRIPTION OF THE INVENTION

A Bandwidth Extender card is plugged into a slot adjacent to a LANService Unit and uses the combined bandwidth of the two slots to providethe doubled bandwidth. Unused I/O lines are used to connect the twounits together across the backplane. These lines are capable of runningLow-voltage differential signaling (LVDS) signals at 622 Mbps or 155Mbps. The BW Extender card receives LVDS signals from the Line Unit (asdo all service unit slots) and relays these signals to the adjacent LANService Unit, effectively doubling the bandwidth available for LANtraffic. The Virtual Concatenation standard is used to take the STSchannels (STS-1 or STS-3c) from the Line Unit interfaces to each of thetwo service unit slots and combines these channels to create a largereffective channel over which LAN traffic can be carried in a SONETencapsulated format. In a similar manner, Link Aggregation techniquescan be used to separate customer traffic into unique conversations thatcan be carried over individual STS channels (STS-1 or STS-3c) from theLine Unit interfaces to each of the two service unit slots, alsocreating a larger effective channel over which LAN traffic can becarried in a SONET encapsulated format. As an example, this method isthe only way to achieve line rate traffic for GigE interfaces, where thebackplane operates at 622 Mbps to each service unit slot.

An exemplary block diagram of a system 100 in which the presentinvention may be implemented is shown in FIG. 1. System 100 includes aWide Area Network 102 (WAN), one or more Local Area Networks 104 and 106(LAN), and one or more LAN/WAN interfaces 108 and 110. A LAN, such asLANs 104 and 106, is computer network that spans a relatively smallarea. Most LANs connect workstations and personal computers. Each node(individual computer) in a LAN has its own CPU with which it executesprograms, but it also is able to access data and devices anywhere on theLAN. This means that many users can share expensive devices, such aslaser printers, as well as data. Users can also use the LAN tocommunicate with each other, by sending e-mail or engaging in chatsessions.

There are many different types of LANs, Ethernets being the most commonfor Personal Computers (PCs). Most Apple Macintosh networks are based onApple's AppleTalk network system, which is built into Macintoshcomputers.

Most LANs are confined to a single building or group of buildings.However, one LAN can be connected to other LANs over any distance vialonger distance transmission technologies, such as those included in WAN102. A WAN is a computer network that spans a relatively largegeographical area. Typically, a WAN includes two or more local-areanetworks (LANs), as shown in FIG. 1. Computers connected to a wide-areanetwork are often connected through public networks, such as thetelephone system. They can also be connected through leased lines orsatellites. The largest WAN in existence is the Internet.

Among the technologies that may be used to implement WAN 102 are opticaltechnologies, such as Synchronous Optical Network (SONET) andSynchronous Digital Hierarchy (SDH). SONET is a standard for connectingfiber-optic transmission systems. SONET was proposed by Bellcore in themiddle 1980s and is now an ANSI standard. The standard defines ahierarchy of interface rates that allow data streams at different ratesto be multiplexed. With the implementation of SONET, communicationcarriers throughout the world can interconnect their existing digitalcarrier and fiber optic systems.

SDH is the international equivalent of SONET and was standardized by theInternational Telecommunications Union (ITU). SDH is an internationalstandard for synchronous data transmission over fiber optic cables.

In this document, a number of embodiments of the present invention aredescribed as incorporating SONET. Although, for convenience, only SONETembodiments are explicitly described, one of skill in the art wouldrecognize that all such embodiments may incorporate SDH and wouldunderstand how to incorporate SDH in such embodiments. Therefore,wherever SONET is used in this document, the use of either SONET or SDHis intended and the present invention is to be understood to encompassboth SONET and SDH.

LAN/WAN interfaces 108 and 110 provide electrical, optical, logical, andformat conversions to signals and data that are transmitted between aLAN, such as LANs 104 and 106, and WAN 102.

An exemplary block diagram of an optical LAN/WAN interface service unit200 (LANSU) is shown in FIG. 2. A typical LANSU interfaces Ethernet to aSONET or SDH network. For example, a Gig/100BaseT Ethernet LANSU mayprovide Ethernet over SONET (EOS) services for up to 4 Gigabit Ethernetports, (4—10/100 BaseT ports in the 100BaseT case). Each port may bemapped to a set of STS-1, STS-3c or STS-12c channels depending onbandwidth requirements. Up to 12—STS-1, 4—STS-3c or 1—STS-12c may besupported up to a maximum of STS-12 bandwidth (STS-3 with OC3 and OC12LUs).

In addition to EOS functions, LANSU 200 may support frame encapsulation,such as GFP, X.86 and PPP in HDLC Framing. High Order VirtualConcatenation or Link Aggregation may be supported for up to 24—STS-1 or8—STS-3c channels and is required to perform full wire speed operationon LANSU 200, when operating at 1 Gbps.

LANSU 200 includes three main functional blocks: Layer 2 Switch 202,ELSA 204 and MBIF-AV 206. ELSA 202 is further subdivided into functionalblocks including a GMII interface 208 to Layer 2 (L2) Switch 202,receive Memory Control & Scheduler (MCS) 210 and transmit MCS 212,encapsulation 214 and decapsulation 216 functions (for GFP, X.86 andPPP), Virtual Concatenation 218, frame buffering provides by memories220, 222, and 224, and SONET mapping and performance monitoringfunctions 226. MBIF-AV 206 is used primarily as a backplane interfacedevice to allow 155 Mbps or 622 Mbps operation. In addition LANSU 200includes physical interface (PHY) 228.

PHY 228 provides the termination of each of the four physical Ethernetinterfaces and performs clock and data recovery, data encode/decode, andbaseline wander correction for the 10/100BaseT copper or 1000Base LX orSX optical. Autonegotiation is supported as follows:

-   -   10/100BaseT—speed, duplexity, PAUSE Capability    -   1 GigE—PAUSE Capability

PHY 228 block provides a standard GMII interface to the MAC function,which is located in L2 Switch 202.

L2 Switch 202, for purposes of transparent LAN services, is operated asa MAC device. L2 Switch 202 is placed in port mirroring mode to providetransparency to all types of Ethernet frames (except PAUSE, which isterminated by the MAC). L2 Switch 202 is broken up into four separate 2port bi-directional MAC devices, which perform MAC level termination andstatistics gathering for each set of ports. Support for Ethernet andEther-like MIBs is provided by counters within the MAC portion of L2Switch 202. L2 Switch 202 also provides limited buffering of frames ineach direction (L2 Switch 202->ELSA 204 and ELSA 204->L2 Switch 202);however, the main packet storage area is the Tx Memory 222 and Rx Memory220 attached to ELSA 204. L2 Switch 202 is capable of buffering 64 to9216 byte frames in its limited memory. Both sides of L2 Switch 202interface to adjacent blocks via a GMII interface.

ELSA 204 provides frame buffering, SONET Encapsulation and SONETprocessing functions.

In the Tx direction, the GMII interface 208 of ELSA 204 mimics PHY 228operation at the physical layer. Small FIFOs are incorporated into GMIIinterface 208 to adapt data flow to the bursty Tx Memory 222 interface.Enough bandwidth is available through the GMII 208 and Tx Memory 222interfaces (8 Gbps) to support all data transfers without frame drop forall four interfaces (especially when all four Ethernet ports areoperating at 1 Gbps). The GMII interface 208 also supports thecapability of flow controlling the L2 Switch 202. The GMII block 208receives memory threshold information supplied to it from the Tx MemoryController 212, which monitors the capacity of the Tx Memory 222 on aper port basis, and is programmable to drop incoming frames or providePAUSE frames to the L2 Switch 202 when a predetermined threshold hasbeen reached in memory. When flow control is used, memory thresholds areset such that no frames will be dropped. The GMII interface 208 mustalso calculate and add frame length information to the packet. Thisinformation is used for GFP frame encapsulation.

The Tx MCS 212 provides the low level interface functions to the TxMemory 222, as well as providing scheduler functions to control pullingdata from the GMII FIFOs and paying out data to the Encapsulation block216.

The primary function of the Tx Memory 222 is to provide a level of bursttolerance to entering LAN data, especially in the case where the LANbandwidth is much greater than the provisioned WAN bandwidth. Asecondary function of this memory is for Jumbo frame storage; thisallows cut through operation in the GMII block 208 to provide for lowerlatency data delivery by not buffering entire large frames. Fixed memorysizes are chosen for each partition regardless of the number of ports orcustomers currently in operation. Partitioning in this fashion preventsdynamic re-sizing of memory when adding or deleting ports/customers andprovides for hitless upgrades/downgrades. The memory is also sizedindependently of WAN bandwidth. This provides for a constant bursttolerance as specified from the LAN side (assuming zero drain rate onWAN side). This partitioning method also guarantees fair allocation ofmemory amongst customers.

The Encapsulation block 216 has a demand based interface to the Tx MCS212. Encapsulation block 216 provides three types of SONET encapsulationmodes, provisionable on a per port/customer basis (although SW may limitencapsulation choice on a per board basis). The encapsulation modes are:

-   -   PPP in HDLC framing    -   X.86    -   GFP (frame mode only)

In each encapsulation mode, additional overhead is added to thepseudo-Ethernet frame format stored in the Tx Memory 222.

The Encapsulation block 216 will decide which of the fields are relevantfor the provisioned encapsulation mode. For example, Ethernet FrameCheck Sequence (FCS) may or may not be used in Point-to-Point (PPP)encapsulation; and, length information is used only in GFPencapsulation. Another function of the Encapsulation block is to provide“Escape” characters to data that appears as High Level Data Link Control(HDLC) frame delineators (7Es) or HDLC Escape characters (7Ds).Character escaping is necessary in PPP and X.86 encapsulation modes. Inthe worst case, character escaping can nearly double the size of anincoming Ethernet frame; as such, mapping frames from the Tx Memory 222to the SONET section of the ELSA 204 is non-deterministic in theseencapsulation modes and requires a demand based access to the Tx Memory222. An additional memory buffer block is housed in the Encapsulationblock 216 to account for this rate adaptation issue. Watermarks areprovided to the Tx MCS 212 to monitor when the scheduler is required topopulate each port/customer space in the smaller memory buffer block.

The Virtual Concatenation (VCAT) block 218 takes the encapsulated framesand maps them to a set of pre-determined VCAT channels. A VCAT channelcan consist of the following permutations:

-   -   Single STS-1    -   Single STS-3c    -   STS-1-Xv (X=1 . . . 24)    -   STS-3c-Xv (X=1 . . . 8)

These channel permutations provide a wide variety of bandwidth optionsto a customer and can be sized independently for each VCAT channel. TheVCAT block 218 encodes the H4 overhead bytes required for properoperation of Virtual Concatenation. VCAT channel composition is signaledto a receive side LANSU using the H4 byte signaling format specified inthe Virtual Concatenation standard. The VCAT block 218 provides TDM datato the SONET processing block after the H4 data has been added.

The SONET Processing block 226 multiplexes the TDM data from the VCATblock 218 into two STS-12 SONET data streams. Proper SONET overheadbytes are added to the data stream for frame delineation, pointerprocessing, error checking and signaling. The SONET Processing block 226interfaces to the MBIF-AV block 206 through two STS-12 interfaces. InSTS-3 mode (155 Mbps backplane interface), STS-3 data is replicated fourtimes in the STS-12 data stream sent to the MBIF-AV 206; the first offour STS-3 bytes in the multiplexed STS-12 data stream represents theSTS-3 data that is selected by the MBIF-AV 206 for transmission.

The MBIF-AV block 206 receives the two STS-12 interfaces previouslydescribed and maps them to the appropriate backplane interface LVDS pair(standard slot interface or BW Extender interface). The MBIF-AV 206 alsohas the responsibility of syncing SONET data to the Frame Pulse providedby the Line Unit and insuring that the digital delay of data from theframe pulse to the Line Unit is within specification. The MBIF-AV 206block also provides the capability of mapping SONET data to a 155 Mbpsor 622 Mbps LVDS interface; this allows LANSU 200 to interface to theOC3LU, OC12LU or OC48LU. 155 Mbps or 622 Mbps operation is provisionableand is upgradeable in system with a corresponding traffic hit. Whenoperating as a 155 Mbps backplane interface, the MBIF-AV 206 must selectSTS-3 data out of the STS-12 stream supplied by the SONET Processingblock and format that for transmission over the 155 Mbps LVDS links.

In the WAN-to-LAN datapath, MBIF-AV 206 is responsible for Clock andData Recovery (CDR) for the four LVDS pairs, at either 155 Mbps or 622Mbps.

The MBIF-AV 206 also contains a full SONET framing function; however,for the most part, the framing function serves as an elastic storeelement for clock domain transfer that is performed in this block. SONETProcessing that is performed in this block is as follows:

-   -   A1, A2 alignment (provides pseudo-frame pulse to SONET        Processing block to indicate start of frame)    -   B1 error monitoring (indicates any backplane errors that may        have occurred)

Additional SONET processing is provided in the SONET Processing block226. Multiplexing of Working/Protect channels from the standard slotinterface or Bandwidth Extender slot interface is also provided in theMBIF-AV block 206. Working and Protect selection is chosen under MCUcontrol. After the proper working/protect channels have been selected,the MBIF-AV block 206 transfers data to the SONET Processing blockthrough one or both STS-12 interfaces. When operating at 155 Mbps, theMBIF-AV 206 has the added responsibility of multiplexing STS-3 data intoan STS-12 data stream which is supplied to the SONET Processing block226.

On the receive side, the SONET Processing block 226 is responsible forthe following SONET processing:

-   -   Path Pointer Processing    -   Path Performance Monitoring    -   RDI, REI processing    -   Path Trace storage

In STS-3 mode of operation (155 Mbps backplane interface), a singlestream of STS-3 data must be plucked from the STS-12 data stream as itenters the SONET Processing block 226. The SONET Processing block 226selects the first of the four interleaved STS-3 bytes to reconstruct thedata stream. After SONET Processing has been completed, TDM data ishanded off to the VCAT block 218.

The VCAT block 218 processing is a bit more complicated on the receiveside because the various STS-1 or STS-3c channels that comprise a VCATchannel may come through different paths in the network—causing varyingdelays between SONET channels. The H4 byte is processed by the VCATblock to determine:

-   -   STS-1 or STS-3c channel sequencing    -   Delays between SONET channels

This information is learned over the course of 16 SONET frames todetermine how the VCAT block 218 should process the aggregate VCATchannel data. As data on each STS-1 or STS-3c is received, it is storedin VC Memory 224. Skews between each STS-1 or STS-3c are compensated forby their relative location in VC Memory 224 based on delay informationsupplied in the H4 information for each channel. The maximum skewbetween any two SONET channels is determined by the depth of the VCMemory 224. Bytes of data are spread one-by-one across each of the SONETchannels that are members of a VCAT channel; so, if one SONET channel islost, no data will be supplied through the aggregate VCAT channel.

The Decapsulation block 214 pulls data out of the VC Memory 224 based onsequencing information supplied to it by the VCAT block 218. Data ispulled a byte at a time from different address locations in VC Memory224 corresponding to each received SONET channel that is a member of theVCAT channel. The Decapsulation block 214 is a Time Division Multiplex(TDM) block that is capable of supporting multiple instances of VCATchannels (up to 24 in the degenerate case of all STS-1 SONET channels)as well as multiple encapsulation types, simultaneously. Decapsulationof PPP in HDLC framing, X.86 and GFP (frame mode) are all supported. TheDecapsulation block 214 strips all encapsulation overhead data from thereceived SONET data and provides raw Ethernet frames to the Rx MCS 210.If Ethernet FCS data was stripped by the transmit side Encap block 216(option in PPP), then it is also added in the Decap block 214. Lengthinformation, used by GFP, will be stripped in this block.

Rx MCS 210 receives data from the Decapsulation block 214 The schedulingfunction required for populating Rx Memory 220 from the SONET side isstraightforward. As the Decapsulation block 214 provides data to Rx MCS210, it writes the corresponding data to memory 220 in the order that itwas received. There is a clock domain transfer from the Decapsulationblock 214 to Rx MCS 210; so, a small amount of internal buffering isprovided for rate adaptation within the ELSA 204. Through provisioninginformation, Rx MCS 210 creates associations of VCAT channels to memorylocations. Four memory partition locations are supported, one for eachpossible LAN port. Data in each memory partition is organized andcontrolled as a FIFO.

The algorithm for scheduling data from the Rx Memory 220 tocorresponding LAN ports is essentially a token-based scheduling scheme.Ports/customers are given a relative number of tokens based on thebandwidth that they are allocated on the WAN side. So, an STS-3c channelis allocated three times as many tokens as an STS-1 channel. Tokens arerefreshed for each port/customer on a regular basis. When the tokensreach a predetermined threshold, a port/customer is allowed to transferdata onto the appropriate LAN port. If the threshold is not reached,additional token replenishment is required before data can be sent. Thisalgorithm takes into account the relative size of frames (byte counts)as well as the allocated WAN bandwidth for a particular port/customer.Each port/customer receives a fair share of LAN bandwidth proportionalto the WAN bandwidth that was provisioned.

The scheduler function also takes into account the possibility of WANoversubscription. Since it is possible to provision an STS-24 worth ofbandwidth, care must be taken when mapping this amount of bandwidth ontoa 1 Gbps LAN link; maintaining fairness of bandwidth allocation amongports/customers is key. The scheduler algorithm provides fairdistribution of bandwidth under these conditions. In the case where WANoversubscription is persistent, Rx Memory 220 will fill and eventuallydata will be discarded; however, it will be discarded fairly, based onthe amount of memory that each port/customer was provisioned.

As with the Tx Memory 222, the Rx Memory 220 is partitioned in the samemanner. Four partitions are created. Each port/customer will get anequal share of memory.

The GMII interface 208 provides the interface to the L2 switch 202 asdescribed earlier for the Tx direction. In the Rx direction, the GMIIinterface 208 supplies PAUSE data as part of the data stream when theGMII has determined that watermarks were crossed in the Tx Memory 222.

The L2 Switch 202 operates the same in the Rx direction as in the Txdirection. It is completely symmetrical and uses port mirroring in thisdirection as well. It may receive PAUSE frames from the GMII I/F 208 inthe ELSA 204, in which case, it will stop sending data to the ELSA 204.In turn, the L2 Switch 202 memory may fill (in the Tx direction) andeventually packets will be dropped, or the L2 Switch 202 will generatePAUSE to the attached router or switch. The L2 Switch 202 supplies thePHY 228 with GMII formatted data.

The PHY 228 converts the GMII information into appropriately codedinformation and performs a parallel to serial conversion and transfersthe data out onto the respective LAN port.

An exemplary block diagram of a system 300 in which the bandwidthextender of the present invention may be implemented is shown in FIG. 3.System 300 includes LANSU 302, Bandwidth Extender Card (BWE) 304,Management & Control Unit (MCU) 306, a plurality of Line Units (LUs),including LU Working 308 and LU Protection 310, and backplane 312. LANSU302 provides the interface between the LAN or LANs connected to LANports 314 and the WAN, such as a SONET network, connected to the WANports 316 of the LUs 308 and 310. For example, LANSU 302 may providefour optical or electrical Ethernet ports 314 via the front panel and a155/622 (STS-3/12) working SONET interface and a 155/622 (STS-3/12)protect SONET interface over backplane 312.

MCU 306 provides management functions to system 300, via interfacingwith local craft ports, SONET Digital Control Channel (DCC), and/orothers. The provided functions include, for example, downloadingconfiguration settings, collection of SONET Performance Monitoringcounts, alarms and outages, and controlling protection switching. EachLU, such as LUs 308 and 310, provides timing control to access precisionnetwork clock, provides SONET frame pulse reference, and can containoptical interfaces to transmit part of all of the SONET data on theSONET network. For example, the LUs may provide OC3/12/48 SONET serviceto a SONET network connected to WAN ports 316.

Backplane 312 provides the signal connectivity among the other parts ofsystem 300 that allow the parts of the system to communicate. Inparticular, backplane 312 provides Management & Control connections 318that allow MCU to control LANSU 302, BWE 304, and LUs 308 and 310. Oneexample of a technology that may be used to provide Management & Controlconnections 318 is the Serial Hardbus.

Backplane 312 also provides data traffic communications connections 320,322, 324, and 326 among LANSU 302, BWE 304, and LUs 308 and 310. EachLANSU, such as LANSU 302 may have interfaces that provide a 155/622(STS-3/12) working SONET connection 320 and a 155/622 (STS-3/12) protectSONET connection 322 to LUs 308 and 310 via backplane 312. BWE 304 isinserted in a LANSU backplane slot and provides a second 155/622(STS-3/12) working SONET connection 324 and a second 155/622 (STS-3/12)protect SONET connection 326 to LUs 308 and 310 via backplane 312.

LANSU 302 has LAN interfaces 314 that provide greater total bandwidththan the single set of SONET working/protect interfaces can handle.Thus, LANSU also provides BWE interfaces 328 and 330, which provide asecond set of SONET working/protect interfaces to BWE 304. Inparticular, BWE interface 328 provides a second 155/622 (STS-3/12)working SONET interface from LANSU 302 to BWE 304 and BWE interface 330provides a second 155/622 (STS-3/12) protect SONET interface from LANSU302 to BWE 304. BWE 304 connects BWE interface 328 to a second 155/622(STS-3/12) working SONET connection 324 to LU 308 via backplane 312 andconnects BWE interface 330 to a second 155/622 (STS-3/12) protect SONETconnection 326 to LU 310 via backplane 312.

Thus, the data traffic communicated over LAN interfaces 314 arecommunicated to LUs 308 and 310 over two backplane SONET connectionseach, which provides double the bandwidth of a single backplane SONETconnection each. The data traffic is routed using virtual concatenation(VCAT), which divides the data traffic into two data streams, each ofwhich is sent over a different one of the two backplane SONETconnections. For example, data traffic received on LAN interface 314 issplit into two data streams, one of which is transmitted over backplaneSONET connections 320 and 322 and the other of which is transmitted viaBWE interfaces 328 and 330 over backplane SONET connections 324 and 326.The two data streams are merged into a single SONET data stream, fortransmission over the SONET network connected to SONET interface 316.The two data streams are reassembled into the original data traffic atthe destination of the SONET network, using VCAT.

Likewise, data received over SONET interface 316 at LUs 308 and 310 is asingle SONET data stream containing two VCAT data streams. LUs 308 and310 divide the single SONET data stream into the two VCAT data streamsand transmit them to LANSU 302 over the two backplane SONET connections.For example, data traffic received on WAN interface 316 is split intotwo data streams, one of which is transmitted over backplane SONETconnections 320 and 322 to LANSU 302 and the other of which istransmitted over backplane SONET connections 324 and 326 to BWE 304 andfrom there to LANSU 302 over BWE interfaces 328 and 330. The two datastreams are reassembled into the original data traffic at LANSU 302,using VCAT, and transmitted over LAN interface 314.

Virtual concatenation (VCAT) is a standard procedure for splitting datainto multiple data streams and recombining the data streams to form theoriginal data. VCAT breaks the integral payload into individual SONETPayload Envelopes (SPEs), separately transports each SPE and thenrecombines them into a contiguous bandwidth at the end point of thetransmission. This type of concatenation requires concatenationfunctionality only at the path termination equipment.

One example of virtual concatenation involves the virtual concatenationof X STS-1/STS-3c SPEs (STS-1/3c-Xv SPE, X=1 . . . 256). For thetransport of payloads that do not fit efficiently into the standard setof synchronous payload envelopes (STS-1 and STS-Nc SPEs) virtualconcatenation can be used.

An STS-1/3c-Xv SPE provides a contiguous payload area of X STS-1/3c SPEwith a payload capacity of X*48960/148608 kbit/s. The payload capacityis mapped into X individual STS-/3c1 SPEs which form the STS-1/3c-XvSPE. Each STS-1/3c SPE has its own POH as specified in 8.2.3. The H4 POHbyte is used for the virtual concatenation specific sequence andmulti-frame indication as defined below.

Each STS-1/3c SPE of the STS-1/3c-Xv SPE is transported individuallythrough the network. Due to different propagation delay of the STS-1/3cSPEs a differential delay will occur between the individual STS-1/3cSPEs. This differential delay has to be compensated and the individualSTS-1/3c SPEs have to be realigned for access to the contiguous payloadarea. The realignment process has to cover at least a differential delayof 125 μs.

Each STS-1/3c SPE of the STS-1/3c-Xv SPE is transported individuallythrough the network. Due to different propagation delay of the STS-1/3cSPEs a differential delay will occur between the individual STS-1/3cSPEs. This differential delay has to be compensated and the individualSTS-1/3c SPEs have to be realigned for access to the contiguous payloadarea. The realignment process has to cover at least a differential delayof 125 μs.

The sequence indicator SQ identifies the sequence/order in which theindividual STS-1/3c SPEs of the STS-1/3c-Xv SPE are combined to form thecontiguous STS-1/3c-Xc SPE payloads. Each STS-1/3c SPE of a STS-1(3c-XvSPE has a fixed unique sequence number in the range of 0 to (X−1). TheSTS-1/3c SPE transporting the first time slot of the STS-1/3c-Xc SPE hasthe sequence number 0, the STS-1/3c SPE transporting the second timeslot the sequence number 1 and so on up to the STS-1/3c SPE transportingtime slot X of the STS-1/3c-Xc SPE with the sequence number (X−1). Thesequence number is fixed assigned and not configurable. It allows theservice provider to check the correct constitution of the STS-1/3c-XvSPE without using the trace. The 8-bit sequence number (which supportsvalues of X up to 256) is transported in bits 1 to 4 of the H4 bytes,using frame 14 (SQ bits 1-4) and 15 (SQ bits 5-8) of the firstmulti-frame stage.

Another example of virtual concatenation involves the virtualconcatenation of X VTn SPEs (n=1.5, 2, 3, 6). For the transport ofpayloads that do not fit efficiently into the standard set ofsynchronous payload envelopes (VT1.5/2/3/6 SPEs) virtual concatenationcan be used.

A VTn-Xv SPE provides a payload area of X VTn SPE payload capacity. Thepayload is mapped in X individual VTn SPEs which form the VTn-Xv SPE.Each VTn SPE has its own POH.

Each VTn SPE of the VTn-Xv SPE is transported individually through thenetwork. Due to this individual transport a differential delay willoccur between the individual VTn SPEs and therefore the order and thealignment of the VTn SPEs will change. At the termination the individualVTn SPEs have to be rearranged and realigned in order to re-establishthe contiguous concatenated container. The realignment process has tocover at least a differential delay of 125 μs.

To perform the realignment of the individual VTn SPEs (n=1.5, 2, 3, 6)that belong to a virtually concatenated group it is necessary to:

-   -   a) Compensate for the differential delay experienced by the        individual VTn SPEs    -   b) To know the individual sequence numbers of the individual VTn        SPEs.

Bit 2 of the Z7 byte of the Low Order VTn POH is used to convey thisinformation from the sending end to the receiving end of the virtuallyconcatenated signal where the realignment process is performed. A serialstring of 32 bits is arranged over 32 four-frame multiframes. Thisstring is repeated every 16 ms (32 bits×500 μs/bit) or every 128 frames.

The LO virtual concatenation information in Z7 bit 2 has a 32 bitsmultiframe. The phase of the LO virtual concatenation information in Z7bit 2 should be the same as for the Z7 bit 1 extended signal label.

Virtually concatenated VTn SPEs must use the extended signal label.Otherwise the frame phase of the Z7 bit 2 multiframe can not beestablished.

The frame consists of the following fields: The LO virtual concatenationframe count is contained in bits 1 to 5. The LO virtual concatenationsequence indicator is contained in bits 6 to 11. The remaining 21 bitsare reserved for future standardization, should be set to all “0”s andshould be ignored by the receiver.

The LO virtual concatenation frame count provides a measure of thedifferential delay up to 512 ms in 32 steps of 16 ms that is the lengthof the multiframe (32×16 ms=512 ms).

The LO virtual concatenation sequence indicator identifies thesequence/order in which the individual VTn SPEs of the VTn-Xv SPE arecombined to form the contiguous VTn-Xc SPE payload capacity. Each VTnSPE of a VTn-Xv SPE has a fixed unique sequence number in the range of 0to (X−1). The VTn SPE transporting the first time slot of the VTn-Xc SPEhas the sequence number 0, the VTn SPE transporting the second time slotthe sequence number 1 and so on up to the VTn SPE transporting time slotX of the VTn-Xc SPE with the sequence number (X−1). For applicationsrequiring fixed bandwidth the sequence number is fixed assigned and notconfigurable. This allows the constitution of the VTn-Xv SPE to bechecked without using the trace.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.For example, the present invention contemplates that the data trafficmay be encapsulated using an encapsulation mode selected from a group ofencapsulation modes comprising Point-to-Point Protocol (PPP), X86, FrameMapped Generic Framing Procedure (GFP-F), Transparent Generic FramingProcedure (GFP-T), Asynchronous Transfer Mode (ATM), Resilient PacketRing (RPR), Ethernet, and Multiprotocol Label Switching (MPLS). Asanother example, the LAN interface of the LAN Service Unit may supportan interface type selected from a group of interface types comprising100 BaseT Ethernet, 1000 BaseT Ethernet, Fiber channel, FiberConnection/Connectivity (FICON), and Enterprise SystemsConnection/Connectivity (ESCON). As another example, the WAN interfaceof the Line Unit supports an interface type selected from a group ofinterface types comprising Synchronous Optical Network (SONET),Synchronous Digital Hierarchy (SDH), Ethernet, and Resilient Packet Ring(RPR). As another example, the backplane data traffic communicationsconnection may be implemented using one of Low-Voltage DifferentialSignaling (LVDS), Low Voltage Positive Emitter Coupled Logic (LVPECL),or Current-Mode Logic (CML).

Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1. A system having increased LAN Service Unit bandwidth comprising: abackplane including a plurality of data traffic communicationsconnections operable to communicate data traffic; a Line Unit includinga WAN interface and a data traffic communications interface to the datatraffic communications connections, the Line Unit operable tocommunicate data traffic between the WAN interface and the data trafficcommunications interface; a LAN Service Unit including a LAN interface,a data traffic communications interface to a Bandwidth Extender, and adata traffic communications interface to the data traffic communicationsconnections, the LAN Service Unit operable to communicate data betweenthe LAN interface and the data traffic communications interface to theBandwidth Extender and to communicate data between the LAN interface andthe data traffic communications interface to the data trafficcommunications connections; and the Bandwidth Extender including a datatraffic communications interface to the LAN Service Unit and a datatraffic communications interface to the data traffic communicationsconnections, the Bandwidth Extender operable to communicate data trafficbetween the data traffic communications interface to the LAN ServiceUnit and the data traffic communications interface to the data trafficcommunications connections.
 2. The system of claim 1, wherein the LANService Unit is further operable to receive data on the LAN interface,split the received data into two data streams, and transmit the dataover the data traffic communications interface to the Bandwidth Extenderand the data traffic communications interface to the data trafficcommunications connections.
 3. The system of claim 2, wherein the LANService Unit is further operable to receive data in two data streams,one data stream received over the data traffic communications interfaceto the Bandwidth Extender and one data stream received over the datatraffic communications interface to the data traffic communicationsconnections, to reassemble the two received data streams into trafficdata, and to transmit the reassembled traffic data over the LANinterface.
 4. The system of claim 3, wherein the LAN Service Unit isfurther operable to split the data received over the LAN interface intomultiple data streams using Virtual Concatenation or Link Aggregation,and wherein the LAN Service Unit is further operable to reassemble themultiple data streams received over the data traffic communicationsinterface to the Bandwidth Extender and over the data trafficcommunications interface to the data traffic communications connectionsusing Virtual Concatenation or Link Aggregation.
 5. The system of claim4, wherein the LAN interface supports Ethernet.
 6. The system of claim5, wherein the WAN interface supports Synchronous Optical Network orSynchronous Digital Hierarchy.
 7. Apparatus for increasing LAN ServiceUnit bandwidth comprising: a Bandwidth Extender including a data trafficcommunications interface to a LAN Service Unit and a data trafficcommunications interface to backplane data traffic communicationsconnections, the Bandwidth Extender operable to communicate data trafficbetween the data traffic communications interface to the LAN ServiceUnit and the data traffic communications interface to the data trafficcommunications connections.
 8. The apparatus of claim 7, wherein thedata traffic communications interface to a LAN Service Unit is operableto communicate data with the LAN Service Unit.
 9. The apparatus of claim8, wherein the data traffic communications interface to the backplanedata traffic communications connections is operable to communicate datawith a Line Unit having a WAN interface.
 10. The apparatus of claim 9,wherein data traffic received from the LAN Service Unit comprises one ofa plurality of data streams formed by the LAN Service Unit by splittingdata received over a LAN interface into two data streams.
 11. Theapparatus of claim 10, wherein data traffic transmitted to the LANService Unit comprises one of a plurality of data streams that arereassembled at the LAN Service Unit to form traffic data and transmittedover the LAN interface.
 12. The apparatus of claim 11, wherein the datatraffic received from the LAN Service Unit has been split using VirtualConcatenation or Link Aggregation, and wherein data traffic transmittedto the LAN Service Unit is reassembled using Virtual Concatenation orLink Aggregation.
 13. The apparatus of claim 12, wherein the LANinterface of the LAN Service Unit supports an interface type selectedfrom a group of interface types comprising Ethernet, 100 BaseT Ethernet,1000 BaseT Ethernet, Fiber channel, FICON, and ESCON.
 14. The apparatusof claim 13, wherein the WAN interface of the Line Unit supports aninterface type selected from a group of interface types comprisingSynchronous Optical Network, Synchronous Digital Hierarchy, Ethernet,and Resilient Packet Ring.
 15. The apparatus of claim 14 wherein thedata traffic is encapsulated using an encapsulation mode selected from agroup of encapsulation modes comprising Point-to-Point Protocol, X86,Frame Mapped Generic Framing Procedure, Transparent Generic FramingProcedure, Asynchronous Transfer Mode, Resilient Packet Ring, Ethernet,and Multiprotocol Label Switching.
 16. The apparatus of claim 12 whereinthe LAN interface of the LAN Service Unit supports an interface typeselected from a group of interface types comprising 100 BaseT Ethernet,1000 BaseT Ethernet, Fiber channel, Fiber Connection/Connectivity, andEnterprise Systems Connection/Connectivity.
 17. The apparatus of claim12 where the backplane data traffic communications connection isimplemented using one of Low-Voltage Differential Signaling, Low VoltagePositive Emitter Coupled Logic, or Current-Mode Logic.